The objective of the proposed research is to study the organization of Ig genes, and their regulated expression through transcription, translation, synthesis of Ig precursor, and formation of the two final products - the secreted Ig and the antigen receptor on lymphoid cells. To study the origin of antibody diversity (germ line or somatic mutation hypotheses) highly labeled nucleic acid probes will be used to quantify V-genes. To get meaningful results it is obligatory to determine the capacity of a distinct V-region probe to quantify V-genes coding for Ig chains of the same and different subgroups. Transcriptional control will be studied by quantification of Ig-mRNA in cells derived from plasmacytoma tumors, and from normal lymphocytes before and after stimulation by mitogens or antigens. Translational control will be studied by looking for factors (to be extracted from appropriate lymphoid cells) that would affect specifically the rate of Ig-mRNA translation in cell-free systems. The balanced (or unbalanced) synthesis of H and L chains will be evaluated from comparing their rate of synthesis with the amount of mRNA coding for each chain. New information on the structure and expression of Ig genes can be obtained from the study of Ig precursors. We have shown that the L-chain mRNA directs the synthesis of a precursor in which two extra peptide-segments are coupled to the amino and carboxyl termini of the mature L-chain. We intend to evaluate the function and relationship of these extra-pieces to the V and C regions of the Ig chain by detemining the size and amino acid sequence of L-chain precursors of different subgroups, searching for possible H-chain precursors, and by studying conversion of the precursor to the mature Ig. Preliminary results show that the NH2-terminal extrapiece belong to the V-region, thus indicating that the V-gene is larger than hitherto known. Furthermore, it seems that the extrapiece would be quite hydrophobic, suggesting that the function of the extrapiece may be to anchor the precursor at the surface membrane of lymphoid cells to serve as the antigen receptor.